Arthroscopic devices and methods

ABSTRACT

A medical device includes an elongated sleeve having a longitudinal axis, a proximal end and a distal end. A cutting member having a plurality of sharp edges is formed from a wear-resistant ceramic material is carried at the distal end of the elongated sleeve. A motor drive is coupled to the proximal end of the elongated sleeve to rotate the sleeve at cutting member at high RPMs to cut bone and other hard tissue. An electrode is carried in a distal portion of ceramic cutting member for RF ablation of tissue when the sleeve and cutting member are is a stationary position. In methods of use, (i) the ceramic member can be engaged against bone and then rotated at high speed to cut bone tissue, and (ii) the ceramic member can be held in a stationary (non-rotating) position to engage tissue and RF energy can be delivered to the electrode to create a plasma that ablates tissue.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/449,796, filed Mar. 3, 2017, now U.S. Pat. No. ______, which is adivisional of U.S. patent application Ser. No. 14/977,256, filed Dec.21, 2015, now U.S. Pat. No. 9,603,656, which claims the benefit ofprovisional application 62/250,315 (Attorney Docket No. 41879-711.101),filed on Nov. 3, 2015, and of provisional application 62/245,796(Attorney Docket No. 41879-710.101), filed on Oct. 23, 2015, the fulldisclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention relates to arthroscopic tissue cutting and removaldevices by which anatomical tissues may be cut and removed from a jointor other site. More specifically, this invention relates to instrumentsconfigured for cutting and removing bone or other hard tissue and havinga ceramic cutting member.

2. Description of the Background Art

In several surgical procedures including subacromial decompression,anterior cruciate ligament reconstruction involving notchplasty, andarthroscopic resection of the acromioclavicular joint, there is a needfor cutting and removal of bone and soft tissue. Currently, surgeons usearthroscopic shavers and burrs having rotational cutting surfaces toremove tissue for such procedures. A typical arthroscopic shaver or burrcomprises a metal cutting member carried at the distal end of a metalsleeve that rotates within an open-ended metal shaft. A suction pathwayfor removal of bone fragments or other tissues is provided through awindow proximal to the metal cutting member that communicates with alumen in the sleeve.

When metal shavers and burrs “wear” during a procedure, which occursvery rapidly when cutting bone, the wear can be accompanied by loss ofmicro-particles from fracture and particle release which occurs alongwith dulling due to metal deformation. In such surgical applications,even very small amounts of such foreign particles that are not recoveredfrom a treatment site can lead to detrimental effects on the patienthealth, with inflammation being typical. In some cases, the foreignparticles can result in joint failure due to osteolysis, a term used todefine inflammation due to presence of such foreign particles. A recentarticle describing such foreign particle induced inflammation isPedowitz, et al. (2013) Arthroscopic surgical tools: “A source of metalparticles and possible joint damage”, Arthroscopy—The Journal ofArthroscopic and Related Surgery, 29(9), 1559-1565. In addition tocausing inflammation, the presence of metal particles in a joint orother treatment site can cause serious problems for future MRIs.Typically, the MRI images will be blurred by agitation of the metalparticles caused by the magnetic field used in the imaging, makingassessments of the treatment difficult.

Another problem with the currently available metal shavers/burrs relatesto manufacturing limitations in combination with the rapid dulling ofmetal cutting edges. Typically, a metal cutter is manufactured bymachining the cutting surfaces and flutes into a burr or abradersurface. The flute shape and geometry can be limited since it isdictated by the machining process, and burr size and shape limitationsmay direct usage toward more coarse bone removal applications. Further,when operated in a rotational or oscillatory mode, the cutting edgesadapted for coarse bone removal may have a kickback effect as the flutesfirst make contact with bone, which is aggravated by rapid dulling ofthe machined cutting edges.

Therefore, the need exists for arthroscopic burrs and/or shavers thatcan operate to cut and remove bone without the release of fracturedparticles and micro-particles into the treatment site. Further, there isa need for burrs/cutters that do not wear rapidly and that can havecutting edges not limited by metal machining techniques.

As an alternative to such arthroscopic cutters and shavers, anotherclass of tissue removal tools relies on radiofrequency (RF) ablation toremove the soft tissue. Tools such as those described in U.S. Pat. Nos.6,149,620 and 7,678,069 can be highly effective in volumetric removal ofsoft tissue in the knee and elsewhere but are ineffective in resectingbone.

Therefore, the need exists for tools that can effectively remove bothbone and soft tissue and which can combine the advantages of bothcutter-based hard tissue resection and RF-based soft tissue ablation. Atleast some of these objectives will be met by the inventions describedbelow.

SUMMARY OF THE INVENTION

The present invention provides a variety of improved tissue removaldevices and methods, including devices and methods which can removetissue by cutting (resection) and/or by radiofrequency (RF) ablation.

In a first specific aspect of the present invention, a medical devicefor removing tissue includes an elongated sleeve having a longitudinalaxis, a proximal end, and a distal end. A ceramic cutting member with atleast one cutting edge extends distally from the distal end of theelongated sleeve, and an electrode is carried by the cutting member. Amotor drive is configured to couple to the proximal end of elongatedsleeve to rotate the cutting member. In some embodiments, the elongatedsleeve is an inner sleeve and is coaxially and rotatably disposed in anouter sleeve, where the outer sleeve may have a cut-out to expose theceramic cutting member and the electrode.

The cutting edge of medical device for removing tissue will have aradially outward rotational periphery which is at least as great as anoutward rotational periphery of the electrode, and the dielectricmaterial typically comprises a wear-resistant ceramic material, usuallyconsisting exclusively of the wear-resistant ceramic material. Exemplarywear-resistant ceramic materials are selected from the group consistingof yttria-stabilized zirconia, magnesia-stabilized zirconia,ceria-stabilized zirconia, zirconia toughened alumina and siliconnitride. The medical device will typically further comprise an RF sourceconnected to the electrode and a controller operatively connectable tothe motor drive, the RF source, and a negative pressure source.

The cutting member of the medical device will often have at least onewindow in a side thereof which communicates with an interior channel ofthe elongated (inner) sleeve which is configured to be connected to anegative pressure source. The window is typically adjacent to theelectrode so that material released by resection and/or ablation can beaspirated through said window. The window optionally can be used forfluid infusion for use in electrosurgery. In some instances, the windowis proximal to the electrode and/or proximal to the cutting edges, an/orat least partly intermediate the cutting edges. The cutting member mayhave from 1 to 100 cutting edges, a diameter ranging between 2 mm and 10mm, and may extend over an axial length ranging between 1 mm and 10 mm.The cutting edges may be arranged in a pattern selected from at leastone of helical, angled and straight relative to said axis.

In a second specific aspect of the present invention, a medical systemfor removing tissue includes an elongated rotatable shaft with a distaltip comprising (or composed of) a ceramic material. A motor drive isconfigured to rotate the shaft and the distal tip, and an electrode iscarried by the distal tip. The electrode is coupled to an RF source, anda controller is operatively connected to the motor drive and to the RFsource. The controller is configured to stop rotation of the shaft in aselected position, such as a position that will expose the electrode ina position that allows it to be used for ablative or other tissuetreatment.

The medical device may further include a sensor configured to sense arotational position of the shaft and to send signals to the controllerindicating said rotational position. The controller may be configured tostop rotation of the shaft in the selected or other position, forexample when a portion of distal tip such as the electrode or cutterelement is properly oriented to perform a desired ablation, resection,or other treatment. The sensor is usually a Hall sensor. The controllermay be further configured to control delivery of RF energy to theelectrode when the shaft in said selected position. The distal tip ofthe rotatable shaft may have at least one window in a side thereof thatopens to an interior channel in the shaft where the channel isconfigured to communicate with a negative pressure source. The windowmay be adjacent the electrode and/or may be at least partly proximal tothe electrode. The distal tip may comprise or consist entirely of awear-resistant ceramic material, such as those listed elsewhere herein.

In a third specific aspect of the present invention, a medical devicefor removing tissue includes an elongated shaft with a distal tip havinga ceramic member. A window in the ceramic member connects to an interiorchannel in the shaft, and an electrode in the ceramic member ispositioned adjacent to a distal end of the window. The interior channelis configured to be coupled to a negative pressure source.

The electrode may have a width equal to at least 50% of a width of thewindow, sometimes being at least 80% of the width of the window, andsometimes being at least 100% of the width of the window, or greater. Atleast one side of the window may have a sharp edge, and the electrodemay at least partly encircle the distal end of the window. The ceramicmember may have at least one sharp edge for cutting tissue, and aradially outward surface of the ceramic member usually defines acylindrical periphery with an outward surface of the electrode beingwithin said cylindrical periphery. The ceramic member will usually haveat least one and more usually a plurality of sharp edges for cuttingtissue.

In a fourth specific aspect of the present invention, a method forelectrosurgical tissue ablation comprises providing an elongated shaftwith a working end including an active electrode carried adjacent to awindow that opens to an interior channel in the shaft. The channel isconnected to a negative pressure source, and the active electrode andwindow are positioned in contact with target tissue in a fluid-filledspace. The negative pressure source may be activated to suction thetarget tissue into the window, and the active electrode is activated(typically to deliver RF energy) to ablate tissue while translating theworking end relative to the targeted tissue.

In specific aspects of the methods, a motor drive rotates the shaft andthe distal tip (typically at at least 3,000 rpm), and a controlleroperatively connects the interior channel to the negative pressuresource and an RF source to the electrode. The ceramic member is awear-resistant material, typically as noted previously herein. Tissuedebris is aspirated through the interior channel, and the working end istranslated to remove a surface portion of the targeted tissue. and/or toundercut the targeted tissue to thereby remove chips of tissue.

In still further aspects, the present invention provides a high-speedrotating cutter or burr that is fabricated entirely of a ceramicmaterial. In one variation, the ceramic is a molded monolith with sharpcutting edges and is adapted to be motor driven at speeds ranging from3,000 rpm to 20,000 rpm. The ceramic cutting member is coupled to anelongate inner sleeve that is configured to rotate within a metal,ceramic or composite outer sleeve. The ceramic material is exceptionallyhard and durable and will not fracture and thus not leave foreignparticles in a treatment site. In one aspect, the ceramic has a hardnessof at least 8 GPa (kg/mm²) and a fracture toughness of at least 2MPam^(1/2). The “hardness” value is measured on a Vickers scale and“fracture toughness” is measured in MPam^(1/2). Fracture toughnessrefers to a property which describes the ability of a materialcontaining a flaw to resist further fracture and expresses a material'sresistance to such fracture. In another aspect, it has been found thatmaterials suitable for the cutting member of the invention have acertain hardness-to-fracture toughness ratio, which is a ratio of atleast 0.5 to 1

While the cutting assembly and ceramic cutting member of the inventionhave been designed for arthroscopic procedures, such devices can befabricated in various cross-sections and lengths and can be use in otherprocedures for cutting bone, cartilage and soft tissue such as in ENTprocedures, spine and disc procedures and plastic surgeries.

In another aspect, the present invention provides a medical device thatincludes an elongated sleeve having a longitudinal axis, a proximal endand a distal end. A cutting member extends distally from the distal endof the elongated sleeve, and has sharp cutting edges. The cutting headis formed from a wear-resistant ceramic material, and a motor coupled tothe proximal end of elongated sleeve rotates the cutting member. Thecutter may be engaged against bone and rotated to cut bone tissuewithout leaving any foreign particles in the site.

The wear-resistant ceramic material may comprise any one or combinationof (1) zirconia, (2) a material selected from the group ofyttria-stabilized zirconia, magnesia-stabilized zirconia and zirconiatoughened alumina, or (3) silicon nitride. The cutting member typicallyhas from 2 to 100 cutting edges, a cylindrical periphery, and is usuallyrounded in the distal direction. The cutting member will typically havediameter ranging from 2 mm to 10 mm, and the cutting edges willtypically extend over an axial length ranging between 1 mm and 10 mm.The cutting edges may be any one of helical, angled or straight relativeto said axis, and flutes between the cutting edges usually have a depthranging from 0.10 mm to 2.5 mm. An aspiration tube may be configured toconnect to a negative pressure source, where the cutting member has atleast one window in a side thereof which opens to a hollow interior. Inthese embodiments, the hollow interior is open to a central passage ofthe elongated member which is connected to the aspiration tube.

In a further aspect, the present invention provides a medical device fortreating bone including an elongated shaft having a longitudinal axis, aproximal end, and a distal end. A monolithic cutting member fabricatedof a material having a hardness of at least 8 GPa (kg/mm²) is coupled tothe distal end of the elongated shaft, and a motor is operativelyconnected to the proximal end of the shaft, said motor being configuredto rotate the shaft at at least 3,000 rpm.

The material usually has a fracture toughness of at least 2 MPam^(1/2),and further usually has a coefficient of thermal expansion of less than10 (1×10⁶/° C.). The material typically comprises a ceramic selectedfrom the group of yttria-stabilized zirconia, magnesia-stabilizedzirconia, ceria-stabilized zirconia, zirconia toughened alumina andsilicon nitride, and the cutting member typically has a cylindricalperiphery and an at least partly rounded periphery in an axialdirection.

In a still further aspect, the present invention provides a medicaldevice for treating bone comprising a monolithic cutting memberfabricated of a material having a hardness-to-fracture toughness ratioof at least 0.5:1, usually at least 0.8:1, and often at least 1:1.

In yet another aspect, the present invention provides a medical devicefor cutting tissue including a motor-driven shaft having a longitudinalaxis, a proximal end, a distal end, and a lumen extending therebetween.A rotatable cutting member is fabricated entirely of a ceramic materialand is operatively coupled to the distal end of the motor-driven shaft.At least one window in the cutting member communicates with the lumen inthe shaft, and a negative pressure source is in communication with thelumen to remove cut tissue from an operative site.

The ceramic material typically has a hardness of at least 8 GPa (kg/mm²)and a fracture toughness of at least 2 MPam^(1/2). Additionally, theceramic material will usually have a coefficient of thermal expansion ofless than 10 (1×10⁶/° C.). Exemplary ceramic materials are selected fromthe group consisting of yttria-stabilized zirconia, magnesia-stabilizedzirconia, ceria-stabilized zirconia, zirconia toughened alumina andsilicon nitride, and the cutting member usually has cutting edges wherethe at least one window is proximate to the cutting edges, and the atleast one window is in at least one flute between the cutting edges.

In another aspect, the present invention provides a method forpreventing foreign particle induced inflammation at a bone treatmentsite. A rotatable cutter fabricated of a ceramic material having ahardness of at least 8 GPa (kg/mm²) and a fracture toughness of at least2 MPam^(1/2) is engaged against bone and rotated to cut bone tissuewithout leaving any foreign particles in the site.

The ceramic material is usually selected from the group consisting ofyttria-stabilized zirconia, magnesia-stabilized zirconia,ceria-stabilized zirconia, zirconia toughened alumina and siliconnitride, and the cutter is typically rotated at 10,000 rpm or greater.Cut bone tissue is removed from the bone treatment site through achannel in the cutter, typically by aspirating the cut bone tissuethrough the channel.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention will now be discussed withreference to the appended drawings. It should be appreciated that thedrawings depict only typical embodiments of the invention and aretherefore not to be considered limiting in scope.

FIG. 1 is a perspective view of a disposable arthroscopic cutter or burrassembly with a ceramic cutting member carried at the distal end of arotatable inner sleeve with a window in the cutting member proximal tothe cutting edges of the burr.

FIG. 2 is an enlarged perspective view of the ceramic cutting member ofthe arthroscopic cutter or burr assembly of FIG. 1.

FIG. 3 is a perspective view of a handle body with a motor drive unit towhich the burr assembly of FIG. 1 can be coupled, with the handle bodyincluding an LCD screen for displaying operating parameters of deviceduring use together with a joystick and mode control actuators on thehandle.

FIG. 4 is an enlarged perspective view of the ceramic cutting membershowing a manner of coupling the cutter to a distal end of the innersleeve of the burr assembly.

FIG. 5A is a cross-sectional view of a cutting assembly similar to thatof FIG. 2 taken along line 5A-5A showing the close tolerance betweensharp cutting edges of a window in a ceramic cutting member and sharplateral edges of the outer sleeve which provides a scissor-like cuttingeffect in soft tissue.

FIG. 5B is a cross-sectional view of the cutting assembly of FIG. 5Awith the ceramic cutting member in a different rotational position thanin FIG. 5A.

FIG. 6 is a perspective view of another ceramic cutting member carriedat the distal end of an inner sleeve with a somewhat rounded distal noseand deeper flutes than the cutting member of FIGS. 2 and 4, and withaspiration openings or ports formed in the flutes.

FIG. 7 is a perspective view of another ceramic cutting member withcutting edges that extend around a distal nose of the cutter togetherwith an aspiration window in the shaft portion and aspiration openingsin the flutes.

FIG. 8 is a perspective view of a ceramic housing carried at the distalend of the outer sleeve.

FIG. 9 is a perspective of another variation of a ceramic member withcutting edges that includes an aspiration window and an electrodearrangement positioned distal to the window.

FIG. 10 is an elevational view of a ceramic member and shaft of FIG. 9showing the width and position of the electrode arrangement in relationto the window.

FIG. 11 is an end view of a ceramic member of FIGS. 9-10 the outwardperiphery of the electrode arrangement in relation to the rotationalperiphery of the cutting edges of the ceramic member.

FIG. 12A is a schematic view of the working end and ceramic cuttingmember of FIGS. 9-11 illustrating a step in a method of use.

FIG. 12B is another view of the working end of FIG. 12A illustrating asubsequent step in a method of use to ablate a tissue surface.

FIG. 12C is a view of the working end of FIG. 12A illustrating a methodof tissue resection and aspiration of tissue chips to rapidly removevolumes of tissue.

FIG. 13A is an elevational view of an alternative ceramic member andshaft similar to that of FIG. 9 illustrating an electrode variation.

FIG. 13B is an elevational view of another ceramic member similar tothat of FIG. 12A illustrating another electrode variation.

FIG. 13C is an elevational view of another ceramic member similar tothat of FIGS. 12A-12B illustrating another electrode variation.

FIG. 14 is a perspective view of an alternative working end and ceramiccutting member with an electrode partly encircling a distal portion ofan aspiration window.

FIG. 15A is an elevational view of a working end variation with anelectrode arrangement partly encircling a distal end of the aspirationwindow.

FIG. 15B is an elevational view of another working end variation with anelectrode positioned adjacent a distal end of the aspiration window.

FIG. 16 is a perspective view of a variation of a working end andceramic member with an electrode adjacent a distal end of an aspirationwindow having a sharp lateral edge for cutting tissue.

FIG. 17 is a perspective view of a variation of a working end andceramic member with four cutting edges and an electrode adjacent adistal end of an aspiration window.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to bone cutting and removal devices andrelated methods of use. Several variations of the invention will now bedescribed to provide an overall understanding of the principles of theform, function and methods of use of the devices disclosed herein. Ingeneral, the present disclosure provides for an arthroscopic cutter orburr assembly for cutting or abrading bone that is disposable and isconfigured for detachable coupling to a non-disposable handle and motordrive component. This description of the general principles of thisinvention is not meant to limit the inventive concepts in the appendedclaims.

In general, the present invention provides a high-speed rotating ceramiccutter or burr that is configured for use in many arthroscopic surgicalapplications, including but not limited to treating bone in shoulders,knees, hips, wrists, ankles and the spine. More in particular, thedevice includes a cutting member that is fabricated entirely of aceramic material that is extremely hard and durable, as described indetail below. A motor drive is operatively coupled to the ceramic cutterto rotate the burr edges at speeds ranging from 3,000 rpm to 20,000 rpm.

In one variation shown in FIGS. 1-2, an arthroscopic cutter or burrassembly 100 is provided for cutting and removing hard tissue, whichoperates in an manner similar to commercially available metals shaversand burrs. FIG. 1 shows disposable burr assembly 100 that is adapted fordetachable coupling to a handle 104 and motor drive unit 105 therein asshown in FIG. 3.

The cutter assembly 100 has a shaft 110 extending along longitudinalaxis 115 that comprises an outer sleeve 120 and an inner sleeve 122rotatably disposed therein with the inner sleeve 122 carrying a distalceramic cutting member 125. The shaft 110 extends from a proximal hubassembly 128 wherein the outer sleeve 120 is coupled in a fixed mannerto an outer hub 140A which can be an injection molded plastic, forexample, with the outer sleeve 120 insert molded therein. The innersleeve 122 is coupled to an inner hub 140B (phantom view) that isconfigured for coupling to the motor drive unit 105 (FIG. 3). The outerand inner sleeves 120 and 122 typically can be a thin wall stainlesssteel tube, but other materials can be used such as ceramics, metals,plastics or combinations thereof.

Referring to FIG. 2, the outer sleeve 120 extends to distal sleeveregion 142 that has an open end and cut-out 144 that is adapted toexpose a window 145 in the ceramic cutting member 125 extending distallyfrom the inner sleeve 122 during a portion of the inner sleeve'srotation. Referring to FIGS. 1 and 3, the proximal hub 128 of the burrassembly 100 is configured with a J-lock, snap-fit feature, screw threador other suitable feature for detachably locking the hub assembly 128into the handle 104 (FIG. 3). As can be seen in FIG. 1, the outer hub140A includes a projecting key 146 that is adapted to mate with areceiving J-lock slot 148 in the handle 104 (see FIG. 3).

In FIG. 3, it can be seen that the handle 104 is operatively coupled byelectrical cable 152 to a controller 155 which controls the motor driveunit 105. Actuator buttons 156 a, 156 b or 156 c on the handle 104 canbe used to select operating modes, such as various rotational modes forthe ceramic cutting member. In one variation, a joystick 158 is movedforward and backward to adjust the rotational speed of the ceramiccutting member 125. The rotational speed of the cutter can continuouslyadjustable, or can be adjusted in increments up to 20,000 rpm. FIG. 3further shows that negative pressure source 160 is coupled to aspirationtubing 162 which communicates with a flow channel in the handle 104 andlumen 165 in inner sleeve 122 which extends to window 145 in the ceramiccutting member 125 (FIG. 2).

Now referring to FIGS. 2 and 4, the cutting member 125 comprises aceramic body or monolith that is fabricated entirely of a technicalceramic material that has a very high hardness rating and a highfracture toughness rating, where “hardness” is measured on a Vickersscale and “fracture toughness” is measured in MPam^(1/2). Fracturetoughness refers to a property which describes the ability of a materialcontaining a flaw or crack to resist further fracture and expresses amaterial's resistance to brittle fracture. The occurrence of flaws isnot completely avoidable in the fabrication and processing of anycomponents.

The authors evaluated technical ceramic materials and tested prototypesto determine which ceramics are best suited for the non-metal cuttingmember 125. When comparing the material hardness of the ceramic cuttersof the invention to prior art metal cutters, it can easily be understoodwhy typical stainless steel bone burrs are not optimal. Types 304 and316 stainless steel have hardness ratings of 1.7 and 2.1, respectively,which is low and a fracture toughness ratings of 228 and 278,respectively, which is very high. Human bone has a hardness rating of0.8, so a stainless steel cutter is only about 2.5 times harder thanbone. The high fracture toughness of stainless steel provides ductilebehavior which results in rapid cleaving and wear on sharp edges of astainless steel cutting member. In contrast, technical ceramic materialshave a hardness ranging from approximately 10 to 15, which is five tosix times greater than stainless steel and which is 10 to 15 timesharder than cortical bone. As a result, the sharp cutting edges of aceramic remain sharp and will not become dull when cutting bone. Thefracture toughness of suitable ceramics ranges from about 5 to 13 whichis sufficient to prevent any fracturing or chipping of the ceramiccutting edges. The authors determined that a hardness-to-fracturetoughness ratio (“hardness-toughness ratio”) is a useful term forcharacterizing ceramic materials that are suitable for the invention ascan be understood form the Chart A below, which lists hardness andfracture toughness of cortical bone, a 304 stainless steel, and severaltechnical ceramic materials.

CHART A Fracture Ratio Hardness Hardness Toughness to Fracture (GPa)(MPam^(1/2)) Toughness Cortical bone 0.8 12  .07:1 Stainless steel 3042.1 228  .01:1 Yttria-stabilized zirconia 12.5 10 1.25:1 (YTZP) YTZP2000 (Superior Technical Ceramics) YTZP 4000 (Superior 12.5 10 1.25:1Technical Ceramics) YTZP (CoorsTek) 13.0 13 1.00:1 Magnesia stabilized12.0 11 1.09:1 zirconia (MSZ) Dura-Z ® (Superior Technical Ceramics) MSZ200 (CoorsTek) 11.7 12 0.98:1 Zirconia toughened 14.0 5 2.80:1 alumina(ZTA) YTA-14 (Superior Technical Ceramics) ZTA (CoorsTek) 14.8 6 2.47:1Ceria stabilized zirconia 11.7 12 0.98:1 CSZ (Superior TechnicalCeramics) Silicon Nitride 15.0 6 2.50:1 SiN (Superior TechnicalCeramics)

As can be seen in Chart A, the hardness-toughness ratio for the listedceramic materials ranges from 98× to 250× greater than thehardness-toughness ratio for stainless steel 304. In one aspect of theinvention, a ceramic cutter for cutting hard tissue is provided that hasa hardness-toughness ratio of at least 0.5:1, 0.8:1 or 1:1.

In one variation, the ceramic cutting member 125 is a form of zirconia.Zirconia-based ceramics have been widely used in dentistry and suchmaterials were derived from structural ceramics used in aerospace andmilitary armor. Such ceramics were modified to meet the additionalrequirements of biocompatibility and are doped with stabilizers toachieve high strength and fracture toughness. The types of ceramics usedin the current invention have been used in dental implants, andtechnical details of such zirconia-based ceramics can be found inVolpato, et al., “Application of Zirconia in Dentistry: Biological,Mechanical and Optical Considerations”, Chapter 17 in Advances inCeramics—Electric and Magnetic Ceramics, Bioceramics, Ceramics andEnvironment (2011).

In one variation, the ceramic cutting member 125 is fabricated of anyttria-stabilized zirconia as is known in the field of technicalceramics, and can be provided by CoorsTek Inc., 16000 Table MountainPkwy., Golden, Colo. 80403 or Superior Technical Ceramics Corp., 600Industrial Park Rd., St. Albans City, Vt. 05478. Other technicalceramics that may be used consist of magnesia-stabilized zirconia,ceria-stabilized zirconia, zirconia toughened alumina and siliconnitride. In general, in one aspect of the invention, the monolithicceramic cutting member 125 has a hardness rating of at least 8 GPa(kg/mm²). In another aspect of the invention, the ceramic cutting member125 has a fracture toughness of at least 2 MPam^(1/2).

The fabrication of such ceramics or monoblock components are known inthe art of technical ceramics, but have not been used in the field ofarthroscopic or endoscopic cutting or resecting devices. Ceramic partfabrication includes molding, sintering and then heating the molded partat high temperatures over precise time intervals to transform acompressed ceramic powder into a ceramic monoblock which can provide thehardness range and fracture toughness range as described above. In onevariation, the molded ceramic member part can have additionalstrengthening through hot isostatic pressing of the part. Following theceramic fabrication process, a subsequent grinding process optionallymay be used to sharpen the cutting edges 175 of the burr (see FIGS. 2and 4).

In FIG. 4, it can be seen that in one variation, the proximal shaftportion 176 of cutting member 125 includes projecting elements 177 whichare engaged by receiving openings 178 in a stainless steel split collar180 shown in phantom view. The split collar 180 can be attached aroundthe shaft portion 176 and projecting elements 177 and then laser weldedalong weld line 182. Thereafter, proximal end 184 of collar 180 can belaser welded to the distal end 186 of stainless steel inner sleeve 122to mechanically couple the ceramic body 125 to the metal inner sleeve122. In another aspect of the invention, the ceramic material isselected to have a coefficient of thermal expansion between is less than10 (1×10⁶/° C.) which can be close enough to the coefficient of thermalexpansion of the metal sleeve 122 so that thermal stresses will bereduced in the mechanical coupling of the ceramic member 125 and sleeve122 as just described. In another variation, a ceramic cutting membercan be coupled to metal sleeve 122 by brazing, adhesives, threads or acombination thereof

Referring to FIGS. 1 and 4, the ceramic cutting member 125 has window145 therein which can extend over a radial angle of about 10° to 90° ofthe cutting member's shaft. In the variation of FIG. 1, the window ispositioned proximally to the cutting edges 175, but in other variations,one or more windows or openings can be provided and such openings canextend in the flutes 190 (see FIG. 6) intermediate the cutting edges 175or around a rounded distal nose of the ceramic cutting member 125. Thelength L of window 145 can range from 2 mm to 10 mm depending on thediameter and design of the ceramic member 125, with a width W of 1 mm to10 mm.

FIGS. 1 and 4 shows the ceramic burr or cutting member 125 with aplurality of sharp cutting edges 175 which can extend helically,axially, longitudinally or in a cross-hatched configuration around thecutting member, or any combination thereof. The number of cutting edges175 ands intermediate flutes 190 can range from 2 to 100 with a flutedepth ranging from 0.10 mm to 2.5 mm. In the variation shown in FIGS. 2and 4, the outer surface or periphery of the cutting edges 175 iscylindrical, but such a surface or periphery can be angled relative toaxis 115 or rounded as shown in FIGS. 6 and 7. The axial length AL ofthe cutting edges can range between 1 mm and 10 mm. While the cuttingedges 175 as depicted in FIG. 4 are configured for optimal bone cuttingor abrading in a single direction of rotation, it should be appreciatedthe that the controller 155 and motor drive 105 can be adapted to rotatethe ceramic cutting member 125 in either rotational direction, oroscillate the cutting member back and forth in opposing rotationaldirections.

FIGS. 5A-5B illustrate a sectional view of the window 145 and shaftportion 176 of a ceramic cutting member 125′ that is very similar to theceramic member 125 of FIGS. 2 and 4. In this variation, the ceramiccutting member has window 145 with one or both lateral sides configuredwith sharp cutting edges 202 a and 202 b which are adapted to resecttissue when rotated or oscillated within close proximity, or inscissor-like contact with, the lateral edges 204 a and 204 b of thesleeve walls in the cut-out portion 144 of the distal end of outersleeve 120 (see FIG. 2). Thus, in general, the sharp edges of window 145can function as a cutter or shaver for resecting soft tissue rather thanhard tissue or bone. In this variation, there is effectively no open gapG between the sharp edges 202 a and 202 b of the ceramic cutting member125′ and the sharp lateral edges 204 a, 204 b of the sleeve 120. Inanother variation, the gap G between the window cutting edges 202 a, 202b and the sleeve edges 204 a, 204 b is less than about 0.020″, or lessthan 0.010″.

FIG. 6 illustrates another variation of ceramic cutting member 225coupled to an inner sleeve 122 in phantom view. The ceramic cuttingmember again has a plurality of sharp cutting edges 175 and flutes 190therebetween. The outer sleeve 120 and its distal opening and cut-outshape 144 are also shown in phantom view. In this variation, a pluralityof windows or opening 245 are formed within the flutes 190 andcommunicate with the interior aspiration channel 165 in the ceramicmember as described previously.

FIG. 7 illustrates another variation of ceramic cutting member 250coupled to an inner sleeve 122 (phantom view) with the outer sleeve notshown. The ceramic cutting member 250 is very similar to the ceramiccutter 125 of FIGS. 1, 2 and 4, and again has a plurality of sharpcutting edges 175 and flutes 190 therebetween. In this variation, aplurality of windows or opening 255 are formed in the flutes 190intermediate the cutting edges 175 and another window 145 is provided ina shaft portion 176 of ceramic member 225 as described previously. Theopenings 255 and window 145 communicate with the interior aspirationchannel 165 in the ceramic member as described above.

It can be understood that the ceramic cutting members can eliminate thepossibility of leaving metal particles in a treatment site. In oneaspect of the invention, a method of preventing foreign particle inducedinflammation in a bone treatment site comprises providing a rotatablecutter fabricated of a ceramic material having a hardness of at least 8GPa (kg/mm²) and/or a fracture toughness of at least 2 MPam^(1/2) androtating the cutter to cut bone without leaving any foreign particles inthe treatment site. The method includes removing the cut bone tissuefrom the treatment site through an aspiration channel in a cuttingassembly.

FIG. 8 illustrates variation of an outer sleeve assembly with therotating ceramic cutter and inner sleeve not shown. In the previousvariations, such as in FIGS. 1, 2 and 6, shaft portion 176 of theceramic cutter 125 rotates in a metal outer sleeve 120. FIG. 8illustrates another variation in which a ceramic cutter (not shown)would rotate in a ceramic housing 280. In this variation, the shaft or aceramic cutter would thus rotate is a similar ceramic body which may beadvantageous when operating a ceramic cutter at high rotational speeds.As can be seen in FIG. 8, a metal distal metal housing 282 is welded tothe outer sleeve 120 along weld line 288. The distal metal housing 282is shaped to support and provide strength to the inner ceramic housing282.

FIGS. 9-11 are views of an alternative tissue resecting assembly orworking end 400 that includes a ceramic or other dielectric member 405with cutting edges 410 in a form similar to that described previously.FIG. 9 illustrates the monolithic ceramic member 405 carried as a distaltip of a shaft or inner sleeve 412 as described in previous embodiments.The ceramic member 405 again has a window 415 that communicates withaspiration channel 420 in shaft 412 that is connected to negativepressure source 160 as described previously. The inner sleeve 412 isoperatively coupled to a motor drive 105 and rotates in an outer sleeve422 of the type shown in FIG. 2. The outer sleeve 422 is shown in FIG.10.

In the variation illustrated in FIG. 9, the ceramic member 405 carriesan electrode arrangement 425, or active electrode, having a singlepolarity that is operatively connected to an RF source 440. A returnelectrode, or second polarity electrode 430, is provided on the outersleeve 422 as shown in FIG. 10. In one variation, the outer sleeve 422can comprise an electrically conductive material such as stainless steelto thereby function as return electrode 445, with a distal portion ofouter sleeve 422 is optionally covered by a thin insulative layer 448such as parylene, to space apart the active electrode 425 from thereturn electrode 430.

The active electrode arrangement 425 can consist of a single conductivemetal element or a plurality of metal elements as shown in FIGS. 9 and10. In one variation shown in FIG. 9, the plurality of electrodeelements 450 a, 450 b and 450 c extend transverse to the longitudinalaxis 115 of ceramic member 405 and inner sleeve 412 and are slightlyspaced apart in the ceramic member. In one variation shown in FIGS. 9and 10, the active electrode 425 is spaced distance D from the distaledge 452 of window 415 which is less than 5 mm and often less than 2 mmfor reasons described below. The width W and length L of window 415 canbe the same as described in a previous embodiment with reference to FIG.4.

As can be seen in FIGS. 9 and 11, the electrode arrangement 425 iscarried intermediate the cutting edges 410 of the ceramic member 405 ina flattened region 454 where the cutting edges 410 have been removed. Ascan be best understood from FIG. 11, the outer periphery 455 of activeelectrode 425 is within the cylindrical or rotational periphery of thecutting edges 410 when they rotate. In FIG. 11, the rotational peripheryof the cutting edges is indicated at 460. The purpose of the electrode'souter periphery 455 being equal to, or inward from, the cutting edgeperiphery 460 during rotation is to allow the cutting edges 410 torotate at high RPMs to engage and cut bone or other hard tissue withoutthe surface or the electrode 425 contacting the targeted tissue.

FIG. 9 further illustrates a method of fabricating the ceramic member405 with the electrode arrangement 425 carried therein. The moldedceramic member 405 is fabricated with slots 462 that receive theelectrode elements 450 a-450 c, with the electrode elements fabricatedfrom stainless steel, tungsten or a similar conductive material. Eachelectrode element 450 a-450 c has a bore 464 extending therethrough forreceiving an elongated wire electrode element 465. As can be seen inFIG. 9, and the elongated wire electrode 465 can be inserted from thedistal end of the ceramic member 405 through a channel in the ceramicmember 405 and through the bores 464 in the electrode elements 450 a-450c. The wire electrode 465 can extend through the shaft 412 and iscoupled to the RF source 440. The wire electrode element 465 thus can beused as a means of mechanically locking the electrode elements 450 a-450c in slots 462 and also as a means to deliver RF energy to the electrode425.

Another aspect of the invention is illustrated in FIGS. 9-10 wherein itcan be seen that the electrode arrangement 425 has a transversedimension TD relative to axis 115 that is substantial in comparison tothe window width W as depicted in FIG. 10. In one variation, theelectrode's transverse dimension TD is at least 50% of the window widthW, or the transverse dimension TD is at least 80% of the window width W.In the variation of FIGS. 9-10, the electrode transverse dimension TD is100% or more of the window width W. It has been found that tissue debrisand byproducts from RF ablation are better captured and extracted by awindow 415 that is wide when compared to the width of the RF plasmaablation being performed.

In general, the tissue resecting system comprises an elongated shaftwith a distal tip comprising a ceramic member, a window in the ceramicmember connected to an interior channel in the shaft and an electrodearrangement in the ceramic member positioned distal to the window andhaving a width that is at least 50% of the width W of the window,usually at least 80% of the width W of the window, and often at least100% of the width W of the window, or greater. Further, the systemincludes a negative pressure source 160 in communication with theinterior channel 420.

Now turning to FIGS. 12A-12C, a method of use of the resecting assembly400 of FIG. 9 can be explained. In FIG. 12A, the system and a controlleris operated to stop rotation of the ceramic member 405 in a selectedposition were the window 415 is exposed in the cut-out 482 of the openend of outer sleeve 422 shown in phantom view. In one variation, acontroller algorithm can be adapted to stop the rotation of the ceramicmember 405 that uses a Hall sensor 484 a in the handle 104 (see FIG. 3)that senses the rotation of a magnet 484 b carried by inner sleeve hub140B as shown in FIG. 2. The controller algorithm can receive signalsfrom the Hall sensor which indicates a rotational position of the innersleeve 412 and ceramic member 405 relative to the outer sleeve 422. Themagnet 484 b (FIG. 3) can be positioned in the hub 140B (FIG. 2) so thatwhen sensed by the Hall sensor, the controller algorithm can de-activatethe motor drive 105 so as to stop the rotation of the inner sleeve inany selected position, e.g. with the window 415 and cut-out 482 aligned.

Under endoscopic vision, referring to FIG. 12B, the physician then canposition the electrode arrangement 425 in contact with tissue targeted Tfor ablation and removal in a working space filled with fluid 486, suchas a saline solution which enables RF plasma creation about theelectrode. The negative pressure source 160 is activated prior to orcontemporaneously with the step of delivering RF energy to electrode425. Still referring to FIG. 12B, when the ceramic member 405 ispositioned in contact with tissue and translated in the direction ofarrow Z, the negative pressure source 160 suctions the targeted tissueinto the window 415. At the same time, RF energy delivered to electrodearrangement 425 creates a plasma P as is known in the art to therebyablate tissue. The ablation then will be very close to the window 415 sothat tissue debris, fragments, detritus and byproducts will be aspiratedalong with fluid 486 through the window 415 and outwardly through theinterior extraction channel 420 to a collection reservoir. In one methodshown schematically in FIG. 12B, a light movement or translation ofelectrode arrangement 425 over the targeted tissue will ablate a surfacelayer of the tissue and aspirate away the tissue detritus.

FIG. 12C schematically illustrates a variation of a method which is ofparticular interest. It has been found if suitable downward pressure onthe working end 400 is provided, then axial translation of working end400 in the direction arrow Z in FIG. 12C, together with suitablenegative pressure and the RF energy delivery will cause the plasma P toundercut the targeted tissue along line L that is suctioned into window415 and then cut and scoop out a tissue chips indicated at 488. Ineffect, the working end 400 then can function more as a high volumetissue resecting device instead of, or in addition to, its ability tofunction as a surface ablation tool. In this method, the cutting orscooping of such tissue chips 488 would allow the chips to be entrainedin outflows of fluid 486 and aspirated through the extraction channel420. It has been found that this system with an outer shaft diameter of7.5 mm, can perform a method of the invention can ablate, resect andremove tissue at a rate greater than 15 grams/min, often greater than 20grams/min, and sometimes greater than 25 grams/min.

In general, a method corresponding to the invention includes providingan elongated shaft with a working end 400 comprising an active electrode425 carried adjacent to a window 415 that opens to an interior channelin the shaft which is connected to a negative pressure source,positioning the active electrode and window in contact with targetedtissue in a fluid-filled space, activating the negative pressure sourceto thereby suction targeted tissue into the window and delivering RFenergy to the active electrode to ablate tissue while translating theworking end across the targeted tissue. The method further comprisesaspirating tissue debris through the interior channel 420. In a method,the working end 400 is translated to remove a surface portion of thetargeted tissue. In a variation of the method, the working end 400 istranslated to undercut the targeted tissue to thereby remove chips 488of tissue.

Now turning to FIGS. 13A-13C, other distal ceramic tips of cuttingassemblies are illustrated that are similar to that of FIGS. 9-11,except the electrode configurations carried by the ceramic members 405are varied. In FIG. 13A, the electrode 490A comprises one or moreelectrode elements extending generally axially distally from the window415. FIG. 13B illustrates an electrode 490B that comprises a pluralityof wire-like elements 492 projecting outwardly from surface 454. FIG.13C shows electrode 490C that comprises a ring-like element that ispartly recessed in a groove 494 in the ceramic body. All of thesevariations can produce an RF plasma that is effective for surfaceablation of tissue, and are positioned adjacent to window 415 to allowaspiration of tissue detritus from the site.

FIG. 14 illustrates another variation of a distal ceramic tip 500 of aninner sleeve 512 that is similar to that of FIG. 9 except that thewindow 515 has a distal portion 518 that extends distally between thecutting edges 520, which is useful for aspirating tissue debris cut byhigh speed rotation of the cutting edges 520. Further, in the variationof FIG. 14, the electrode 525 encircles a distal portion 518 of window515 which may be useful for removing tissue debris that is ablated bythe electrode when the ceramic tip 500 is not rotated but translatedover the targeted tissue as described above in relation to FIG. 12B. Inanother variation, a distal tip 500 as shown in FIG. 14 can be energizedfor RF ablation at the same time that the motor drive rotates back andforth (or oscillates) the ceramic member 500 in a radial arc rangingfrom 1° to 180° and more often from 10° to 90°.

FIGS. 15A-15B illustrate other distal ceramic tips 540 and 540′ that aresimilar to that of FIG. 14 except the electrode configurations differ.In FIG. 15A, the window 515 has a distal portion 518 that again extendsdistally between the cutting edges 520, with electrode 530 comprising aplurality of projecting electrode elements that extend partly around thewindow 515. FIG. 15B shows a ceramic tip 540′ with window 515 having adistal portion 518 that again extends distally between the cutting edges520. In this variation, the electrode 545 comprises a single bladeelement that extends transverse to axis 115 and is in close proximity tothe distal end 548 of window 515.

FIG. 16 illustrates another variation of distal ceramic tip 550 of aninner sleeve 552 that is configured without the sharp cutting edges 410of the embodiment of FIGS. 9-11. In other respects, the arrangement ofthe window 555 and the electrode 560 is the same as describedpreviously. Further, the outer periphery of the electrode is similar tothe outward surface of the ceramic tip 550. In the variation of FIG. 16,the window 555 has at least one sharp edge 565 for cutting soft tissuewhen the assembly is rotated at a suitable speed from 500 to 5,000 rpm.When the ceramic tip member 550 is maintained in a stationary positionand translated over targeted tissue, the electrode 560 can be used toablate surface layers of tissue as described above.

FIG. 17 depicts another variation of distal ceramic tip 580 coupled toan inner sleeve 582 that again has sharp burr edges or cutting edges 590as in the embodiment of FIGS. 9-11. In this variation, the ceramicmonolith has only 4 sharp edges 590 which has been found to work wellfor cutting bone at high RPMs, for example from 8,000 RPM to 20,000 RPM.In this variation, the arrangement of window 595 and electrode 600 isthe same as described previously. Again, the outer periphery ofelectrode 595 is similar to the outward surface of the cutting edges590.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.

1. (canceled)
 2. A medical device for resecting tissue comprising: anelongated outer sleeve assembly extending about a longitudinal axis witha distal region having an opening that extends to a bore therein; and aninner sleeve assembly with a distal ceramic cutting member having aplurality of cutting edges defining a cylindrical periphery, the ceramiccutting member adapted to rotate in the opening of the outer sleeveassembly; an electrode carried by the ceramic cutting member on asurface between cutting edges; and a motor drive configured to couple tothe inner sleeve assembly to rotate the ceramic cutting member.
 3. Themedical device of claim 2, wherein the electrode has a curved surface.4. The medical device of claim 3, wherein the curved surface of theelectrode is has a radius relative to the longitudinal axis similar tothe radius relative to the longitudinal axis. of the cylindricalperiphery of the cutting edges.
 5. The medical device of claim 3,wherein the cylindrical periphery of the cutting edges has a radiusrelative to the longitudinal axis which is at least as great as a radiusof a periphery of a surface carrying the electrode relative to thelongitudinal axis.
 6. The medical device of claim 2, wherein the ceramiccutting member comprises a wear-resistant ceramic material.
 7. Themedical device of claim 4, wherein the wear-resistant ceramic materialis selected from the group consisting of yttria-stabilized zirconia,magnesia-stabilized zirconia, ceria-stabilized zirconia, zirconiatoughened alumina and silicon nitride.
 8. The medical device of claim 2,further comprising an RF source connected to the electrode and acontroller operatively connected to the motor drive and the RF source.9. The medical device of claim 2, wherein the ceramic cutting member hasfrom 2 to 100 cutting edges.
 10. The medical device of claim 2, whereinthe ceramic cutting member has a diameter ranging between 2 mm and 10mm.
 11. The medical device of claim 2, wherein the cutting edges ofceramic cutting member extend over an axial length ranging between 1 mmand 10 mm.
 12. The medical device of claim 2, wherein the cutting edgesare arranged in a pattern selected from at least one of helical, angledand straight relative to the axis.
 13. The medical device of claim 2,wherein a gap between the cutting edges of the ceramic cutting memberand a wall of the opening of the outer sleeve assembly is less than0.020″.
 14. The medical device of claim 2, wherein the gap between thecutting edges of the ceramic cutting member and the wall of the openingof the outer sleeve assembly is less than 0.010″.
 15. The medical deviceof claim 2, further comprising a negative pressure source coupled to thebore in the outer sleeve assembly.